1. Field of the Invention
The present invention relates to storage systems, and more particularly, to maintaining data integrity in storage systems.
2. Background of the Invention
Conventional storage systems (disk drive etc.) store data bytes in sets of predetermined length. Disk array storage systems have multiple storage disk drive devices that are arranged and managed as a single mass storage system. Redundancy is often used to aid data availability, where data or data relationship is stored in multiple locations. In the event of a failure, redundant data is retrieved from the operable portion of a system and used to regenerate the lost data. A RAID (Redundant Array of Independent Disks) storage system is one such system that uses a part of the physical storage capacity to store redundant data.
Data is typically moved from plural host systems (that include computer systems, and embedded devices etc.) to the storage system through a RAID controller.
Various standard interfaces are used to move data from host systems to storage devices. Fibre channel is one such standard. Fibre channel (incorporated herein by reference in its entirety) is an American National Standard Institute (ANSI) set of standards which provides a serial transmission protocol for storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users.
Host systems often communicate via a host bus adapter (“HBA”) using the “PCI” bus interface. PCI stands for Peripheral Component Interconnect, a local bus standard that was developed by Intel Corporation®. The PCI standard is incorporated herein by reference in its entirety. Most modern computing systems include a PCI bus in addition to a more general expansion bus (e.g. the ISA bus). PCI is a 64-bit bus and can run at clock speeds of 33 or 66 MHz.
PCI-X is a standard bus that is compatible with existing PCI cards using the PCI bus. PCI-X improves the data transfer rate of PCI from 132 MBps to as much as 1 GBps. The PCI-X standard was developed by IBM®, Hewlett Packard Corporation® and Compaq Corporation® to increase performance of high bandwidth devices, such as Gigabit Ethernet standard and Fibre Channel Standard, and processors that are part of a cluster.
The iSCSI standard (incorporated herein by reference in its entirety) is based on Small Computer Systems Interface (“SCSI”), which enables host computer systems to perform block data input/output (“I/O”) operations with a variety of peripheral devices including disk and tape devices, optical storage devices, as well as printers and scanners. A traditional SCSI connection between a host system and peripheral device is through parallel cabling and is limited by distance and device support constraints. For storage applications, iSCSI was developed to take advantage of network architectures based on Fibre Channel and Gigabit Ethernet standards. iSCSI leverages the SCSI protocol over established networked infrastructures and defines the means for enabling block storage applications over TCP/IP networks. iSCSI defines mapping of the SCSI protocol with TCP/IP.
The iSCSI architecture is based on a client/server model. Typically, the client is a host system such as a file server that issues a read or write command. The server may be a disk array that responds to the client request.
When data is moved to/from host systems to/from disk storage systems at high data rates, (e.g., 2 GBps), it is essential to maintain data integrity to take advantage of the high bandwidth that is offered by current industry standards.
Cyclic redundancy check (“CRC”) is one way to maintain and validate data integrity. CRC bytes are generated and stored for each data set. CRC involves a process that operates on a block of data and generates a number (called checksum) that represents the content and organization of the data block. CRC is performed on data so that by comparing the checksum of a block of data to the checksum of another block of data, an exact match can be found. CRC is performed when data files are transferred from one location to another (host to storage/storage to host).
CRC calculations themselves are well known in the art. However, conventional techniques do not provide complete data integrity via CRC because often CRC is performed either too late or too early in the data transfer process.
Therefore, there is a need for a system and method that can provide data integrity for modern storage systems that are operating in high band-width environment.